By Darren Hefty

2016 has been a bad year for corn rootworm control. There are 4 big reasons why.

  1. An increase in conventional corn acres
  2. Some farmers cutting back or eliminating planting time insecticide
  3. A switch from SmartStax to above ground only Bt’s
  4. A mild winter

How do you gauge the type of rootworm pressure you had earlier this year? There are three ways.

  1. The rootworm beetles that are in your corn and soybean fields now are the adult stage of the corn rootworm larvae that fed on your corn roots earlier this season.  If you’re seeing lots of them, you really had a problem. 
  2. Lodging in your corn field is a sign of a poor root system or a poor stalk.  If there was heavy feeding on the roots, corn rootworm is likely the culprit.
  3. Do some root digs.  Earlier in the season, you could dig up corn roots and actually see the little white larvae of the corn rootworm eating your root system.  Now, you can see the end result of their feeding.  Depending on how many rings of nodal roots got eaten off, the industry has a rating scale used to show the severity of the problem.  If there’s enough feeding to notice, you need to do something.

What Can You Do Now?

This is the easiest and most obvious solution . . . SPRAY THE BEETLES!  To lessen rootworm pressure next year, you can spray the beetles now, but you need to do it quickly.  Once the beetles have laid eggs on or in the soil, your spray application becomes little more than a revenge kill.  Sure, in the unlikely event that there is an overwhelming amount of beetles in your field, you could stop them from feeding on corn silks.  If all the silks get clipped off before pollination, you will have ears with no kernels on them.  I’m not trying to scare you about that, but it does happen to someone almost every year.

In terms of products that can kill corn rootworm beetles, there are many.  The cheaper pyrethroids like Silencer (2.56-3.84 oz/acre) and Mustang Maxx (2.72 to 4.0 oz/acre) are highly effective even at lower rates and only cost a couple bucks an acre or less.  Be sure to scout before treating as you could add a tankmix partner like a foliar feed or a fungicide with it to save a trip.  Also, be on the lookout for spider mites, especially if you’ve been hot and dry.  You may need to switch to a bifenthrin product like Brigade or a combination product like Hero or even a chlorpyrifos like Lorsban Advanced to control them.  If those options are not effective in your area, a miticide may be used instead, but the miticide may not kill your rootworm beetles.

Corn rootworm beetles normally aren’t a huge threat themselves, but they lay eggs for next year’s corn rootworm larvae, so get them under control now to lessen your rootworm pressure next year.  If you’ve had a bad rootworm issue this year, you’ll need to consider going back to rootworm Bt corn or using a planting-time insecticide next year.